Radio-frequency transmitter



RADIO FREQUENCY TRANSMITTER Filed June 22, 1942 DONALD L. WNGS INVENTOR ATTOR /M s Patented Feb. 11, 1947 2,415,427 RADIO-FREQUENCY TRANSMITTER Donald L. Hings, Ottawa, Ontario, Canada, assignor to Electronic Laboratories, Inc., Indianapolis, Ind, a corporation of Indiana Application June 22, 1942, Serial No. 447,890

11 Claims.

This application is an improvement on my pending application, Serial No. 412,708, filed September 29, 1941.

My invention relates in general to radio frequency systems and more particularly to a transmitter system for energizing an antenna.

An object of my invention is to provide for operating a thermionic tube in a transmitter system at a high efficiency.

Another object of my invention is the provision of operating a thermionic tube in a resonant output circuit having a high impedance wherein the tube is operated to produce a thermionic reactance to render the tube highly eflicient.

Another object of my invention is the provision of operating a thermionic tube to cause a misalignment of the peak voltage impressed upon the output thereof and the peak voltage impressed upon the input of the tube.

Another object of my invention is to provide for utilizing the cathode of a tube as a control element in conjunction with the grid and for supplying the cathode with a radio frequency source of energy of a sufiicient value that the tube is caused to not only pass amplified current but also to pass energy between the cathode and plate as a conducted radio frequency current.

Another object of my invention is to provide for coupling the amplifier tube of my transmitter system with the radio frequency source through means of a tuned coupler.

Another object of my invention is to provide for operating the amplifier tube as athermionic reactance in the output circuit of my system.

Another object of my invention is to accomplish a thermionic reactance effect within the amplifying tube by causing a conducted radio frequency current to flow therein in addition to the amplified current.

Other objects and a fuller understanding of my invention may be had by referring to the following description and claims taken in conjunction with the accompanying drawing in which Figure 1 is a diagrammatic view of a circuit embodying the features of my invention. Figure 2 is a fragmentary view showing a modified tuned coupler used in my system. Figure 3 is a fragmentary view of my circuit showing a still further modified coupler."

With reference to Figure 1 of the drawing, my invention comprises generally a thermionic tube which supplies the radio frequency energy, an amplifying thermionic tube H which is coupled to receive energy from the. tube I0 through a tuned coupler indicated generally by the reference character I4. The thermionic tube II is arranged to supply and control radio frequency energy to the antenna l2. As illustrated, the energy in the amplifying tube I! may be modulated by the microphone l3. In my invention, any suitable radio frequency source may be employed and as illustrated I employed a cathode feedback oscillator wherein the frequency of the oscillations is governed by an oscillatory circuit comprising an inductance l9 and a condenser 20. The tube it may be of any suitable design and I find from experience that a beam type of tube works very satisfactorily. In the drawing the reference character 30 represents beam forming plates which are connected to ground, shielding the input and output circuits. The screen grid is designated by reference character I! and is likewise connected to ground for radio frequency by a by-pass condenser l8. The grid l6 of the tube Ill is maintained at a negative bias by means of a grid leak resistor 22 which is shunted by a grid condenser 21. The cathode I5 is shown as a filament type but it is to be understood that the indirectly heated cathode type may be used with the same degree of effectiveness. The energy for heating the cathode is obtained from the filament battery 25 and current may flow from the battery 25 through a circuit including a conductor 24, a winding 26, the filament l5 and to a tapped connection 21 on the oscillatory inductance I9 and then through the lower'portion of the windings to ground. The winding 26 receives radio frequency energy from the oscillatory inductance I9 and together with the tapped connection '21 supplies radio frequency energy on the cathode. The screen grid I'd functions as a plate for the return of the radio frequency voltage in the oscillatory circuit. The action of the tube I!) is such as to produce a radio frequency voltage to the tuned coupler it which in turn supplies energy to the amplifier thermionic tube H. The resistor 28 is arranged to limit the screen grid current or dissipation of power. The oscillations of'the tube H! produce a rectified radio frequency current in which the direct current component is filtered by flowing through a radio frequency choke 3! to the positive side of a plate battery 32. The direct current component of th rectified radio frequency current is prevented from flowing to the tuned coupler by a plate blocking condenser 33. The radio frequency energy from the plate 29 of the tube l0 flows through the condenser 33 to the tuned coupler it which comprises a parallel combination of a tapped inductance 34 and a variable condenser 35, The coupler l4 may be tuned to substantial resonance by the variable condenser 35.

The cathode 45 of the amplifying tube ll receives radio frequency energy from the tuned coupler l4. In Figure l, the cathode 45 receives radio frequency driving energy from the tuned coupler 14 by means of a winding 4! which is inductively coupled to the inductance 34. The voltage across the winding 4i and the radio frequency voltage on the lower portion of the inductance 34 below the tap 44 is of substantially the came value so that the voltage impressed upon each side of the cathode 45 is substantially the same. The filament cathode 45 is energized from the filament battery 25 through conductors 24, 42 and 43, the winding M, the filament of the cathode 45, and returns to ground through the tapped connection 44 and the lower portion of the inductance 34. The grid 45 of the tube l l is maintained at substantially a constant negative bias by being connected to the negative potential of the grid bias battery 53, through the secondary winding of a microphone transformer 52 and is maintained substantially at radio frequency ground potential through a grid by-pass condenser 5|. The screen grid 41 is maintained at a constant potential with respect to ground through the by-pass condenser 48. A resistor 49 which is connected to the screen grid 41 and serves to limit the screen grid current. The tube ll may be of any suitable type and I find from practice that a beam type tube works very successfully. The beam form plates of the tube are illustrated by the reference characters 51 and are connected to ground, thereby isolating the input and output circuits. The tube ll when in operation delivers a rectified radio frequency amplified current to the plate 56, in which the rectified direct current is filtered through a radio frequency choke 58 and passes through conductors 50 and 37 to the positive side of the plate battery 32, the condenser 59 blocking the direct current potential. The radio frequency voltage from the plate 56 is coupled to the variable inductance 6| which resonates the antenna circuit including the antenna l2 and the condenser 60. The antenna circuit is of the series loaded resonant type, with one end of the circuit tuned to ground through the condenser 60 and the other end open to the antenna. This type of open oscillatory circuit possesses a high impedance to ground with respect to the plate 55 of the tube I.

The radio frequency potential of the cathode 45 is responsive to the current flowing in the output antenna system in addition to the energy supplied to it from the tuned coupler I4. The energiz'ation from the tuned coupler I4 and from the responsive action from the output antenna system is cumulative.' The responsive energization upon the cathode from th outputantenna system results from the fact that the cathode is maintained at a radio frequency potential above ground and is coupled to the plate 55 by thermionic reactance of the tube ll. While I do not want to be bound by the consequences of a theory it is my belief that the thermionic reactance in the tube l l exists by rgeason of the fact that the cathode is driven hard, that is heavily enerconducted radio frequency current, which when taken together with a high impedanc output cirupon the cathode 45. piers may be employed and accordingly I have illustrated two such types in Figures 2 and 3. In

cuit having a high electrical inertia, causes a time factor displacement of the radio frequency plate voltage with respect to the radio frequency cathode voltage. The relationship between the amplified current and the conducted radio frequency current in the tube enables the peak of the negative swing of the radio frequency voltage of the plate, which tends to reach a high peak value because of the high impedance of the output circuit and the antenna, to miss the voltage peak resulting from the potential difference between the cathode and the grid on the negative swing of the cathode radio frequency voltage which produced the negative swing on the plate. This misalignment of the approaching peak voltage allows a larger radio frequency voltage to exist, and accordingly a larger output energy to be delivered by the tube than could be produced without the occurrence of this misalignment or the time factor displacement. Actual tests appear to support the above described theory because when instruments are inserted in the circuit, readings show that a misalignment or time factor displacement occurs between the radio frequency voltage on the plate 56 and the radio frequency voltage impressed upon the cathode 46.

In the operation of my circuit when there is no modulation from the microphone l3 the tube is working at low power. As modulation from the microphone I3 is impressed upon the tube the tube then delivers mor power under which condition if the power load becomes extremely heavy the approaching peak voltages in the tube became misaligned with each other so that the swing of the radio frequency energy may reach a high value which high value would be otherwise precluded if there were no misalignment between the peaks of the approaching voltages. Actual tests show that the tube H when connected in a system as illustrated and operated as a class C amplifier possesses a high efliciency in a range of the neighborhood of whereas the efficiency of a modulated amplifier with no thermionic reactance present is normally in a range of the neighborhood of 33 Another feature of my invention is that the action is cumulative and that there is no wilting or decaying of the power energy delivered by the tube on the peaks of heavy modulation resulting from signals being transmitted to the microphone 13. In other words, my entire system is stable and in the circuit illustrated the stability of my system is obtained by the combined action of several component parts. One of the provisions which aids in rendering my circuit stable is that I employ a tuned coupler 14 between the radio frequency source and the amplifier. The tuned coupler circuit may be tuned to a harmonic of the radio frequency source to isolate the amplifier circuit from the radio frequency source. Another feature which lends stability to my circuit is that I operate the oscillatory tube 10 in a cathode feed-back oscillatory circuit. In addition a certain amount of stability is given to my circuit by maintaining the beam form plates in the tubes substantially at ground potential.

The inductance element 34 of the tuned coupler l4 may be provided with taps to vary the amount of radio frequency voltage impressed Other types of tuned cou- Figure 2 the coupler is indicated by reference character 55 and comprises an inductance element 64 which takes the place of the inductance 34 in Figure 1, with the variable condenser .35 being still employed. The coupler 55 is substantially tuned to resonance by the variable condenser 35. The voltage of the coupler 55 is impressed upon the cathode 45 by means of two windings 62 and 63 which are inductively coupled to the inductance element 64. The winding 62 is comparable to the winding 4! and the winding 63 is added so that the radio frequency potential applied to each .side of the cathode is substantially the same.

In Figure 3 the tuned coupler is,indicated by the reference character 68 and comprises an inductance element 69 and two condensers iii and 1| having a tap connection 12 therebetween connected to the cathode 65 of the tube which is connected to ground through the radio frequency choke B1. In Figure 3, I illustrate an indirectly heated type of cathode which may with equal facility be used in my circuit as well as the filament type of cathode illustrated. In other words,

in my invention the filament type of cathode may be readily interchanged with the indirectly heated cathode. The tuned coupler 68 maybe tuned to substantial resonance by the condensers l0 and H- wherein the ratio between the value of the capacitance of the condensers l0 and H control the amount of radio frequency voltage impressed upon the cathode of the amplifier tube.

I have shown three arrangements for the tuned coupler but it is understood that a large number of variations may be employed by matching one or more condensers with one or more inductances which creates exactly the same results as those brought about by the illustrated couplers.

In the drawing I have illustrated a microphone type of signal input but it is to be understood that any type of signal input may be employed besides the microphone. Accordingly in this application the designation of a signal input means any type of intelligence used in its broadest sense. While I have illustrated batteries to supply energy to the component parts of the circuit it is to be understood that these batteries may be replaced by any suitable means of power supply.

Although I have shown and described my invention with a certain degree of'particularity, it is understood that changes may be made therein without departing from the spirit of the invention which are included within the scope of claims hereinafter set forth.

I claim as my invention:

1. An electrical system for operating a thermionic tube to render the tube highly eflicient comprising, in combination, resonant oscillatory output circuit means energized by the tube, said tube having electron emitting means, a source of radio frequency, input circuit means including coupling means for energizing the emitting means of the tube at high frequency potentials above ground, and grid control means for controlling the said thermionic tube to render the resonant oscillatory output circuit means out of resonance with the frequency of the input means, said coupling means comprising a parallel combination of inductance means and capacitor means, and reactively interconnecting the source of radio frequency oscillations to the output circuit for re" actively transferring energy therebetween, and including winding means magnetically coupled to the inductance means for connecting the coupling means to the electron emitting means of the tube.

iii)

2. ,An electrical system for operating .a thermionic tube to render the tube highly efficient comprising, in combination, resonant oscillatory output circuit means energized by the tube, said tube having electron emitting means, a source of radio frequency, input circuit means including coupling means for energizing the emitting means of the tube at high frequency potentials above ground, the grid control means for controlling the said thermionic tube to render the resonant oscillatory output circuit means out of resonance with the frequency of the input means, said coupling means comprising a parallel combination of inductance means and capacitor means, and reactively interconnnecting the source of radio fre quency oscillations to the output circuit for reactively transferring energy therebetween, the ca pacitor means comprising a plurality of capacitors having tapped connections between them for connecting the coupling means to the electron emitting means of the tube.

3. A radio frequency system comprising a source of radio frequency oscillations including an oscillator tube having at least electron emitting means and electron receiving means, a driven tube having electron emitting means, electron receiving means and control means, means for maintaining the electron receiving means for both tubes at radio frequency potentials above ground, reactive coupling means connected between the electron receiving means of the oscillator tube and ground, said coupling means including inductance means and capacitor means connected in parallel and tuned to substantial resonance, connection means for connecting the coupling means to the electron emitting means of the driven tube and energizing the electron emitting means at radio frequency potentials above ground, output circuit means including a series resonant circuit, effective alternating current connection means for connecting said output circuit means to the electron receiving means of the driven tube, said output circuit means being energized by current appearing between the electron receiving means of the driven tube and ground, and means for applying modulating potentials to the control means of the driven tube, said coupling means and said connection means reactively interconnecting the source of radio frequency oscillations and the output circuit means for reactively transferring energy therebetween, and nonresonant circuit means for connecting the control means to ground.

4. A radio frequency system comprising a source of radio frequency oscillations including an oscillator tube having at least electron emitting means and electron receiving means, a driven tube having electron emitting means, electron receiving means and control means, means for maintaining the electron receiving means for both tubes at radio frequency potentials above ground, reactive coupling means connected between the electron receiving means of the oscillator tube and ground, said coupling means including inductance means and capacitor means connected in parallel and tuned to substantial resonance, winding means magnetically coupled to the inductance means for connecting the cou pling means to the electron emitting means of the driven tube and energizing the electron emitting means at radio frequency potentials above ground, output circuit means including a series resonant circuit, efiective alternating current connection means for connecting said output circuit means to the electron receiving means of the driven tube, said'output circuit means being energized by current appearing between the elec' tron receiving means of the driven tube and ground, and means for applying modulating potentialsto the control means of the driven tube, said coupling means and said connection means reactively interconnecting the source of radio frequency oscillations and the output circuit means for reactively transferring energy therebetween. 5. A radio frequency system comprising a source of radio frequency oscillations including an oscillator tube having at least electron emitting means and electron receiving means, a driven tube having electron emitting means, electron receiving means and control means, means for maintaining the electron receiving means for both tubes at radio frequency potentials above ground, reactive coupling means connected between the electron receiving means of the oscillator tube and ground, said coupling means including inductance means and capacitor means connected in parallel and tuned to substantial resonance, said capacitor means comprising a plurality of capacitors having a tapped connection means between them, connection means for connecting the tapped connection means to the electron emitting means at radio frequency potentials above ground, output circuit means including a series resonant circuit, effective alternating current connection means for connecting said output circuit means to the electron receiving means of the driven tube, said output circuit means being energized by current appearing between the electron receiving means of the driven tube and ground, and means for applying modulating potentials to the control means of the driven tube, said coupling means and said connection means reactively interconnecting the source of radio frequency oscillations and the output circuit means for reactively transferring energy therebetween.

6. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode, and a control electrode, a source of carrier frequency for exciting the cathode with respect to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, said series resonant circuit including inductance means and radio frequency radiating means having a capacitance with respect to said point, said inductance means having first and second ends, effective alternating current connection means for connecting the said first end of the-inductance means to the said anode, electrical conducting means for connecting said second end of the inductance means to the said radio frequency radiating means, and means including capacitance means interconnecting said first end and said point of reference potential for by-passing radio frequency energy therebetween to alter the energy supplied to the series resonant circuit.

'7. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode, and a control electrode, a source of carrier frequency, radio frequency connecting means for connecting the cathode to the source of carrier frequency for exciting the cathode with respect to a point of reference potential, a load circuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing betwen said anode and said point, said series resonant circuit including an inductance element and radio frequency'radiating' means having a capacitance with respect to said point, said inductance element having first and second ends, effective alternating current connection means for connecting the said first end of the inductance means to the said anode, electrical con-- ducting means for connecting said second end of the inductance means to the said radio'frequency radiating means, and means including a capacitance element interconnecting said first end and said point of reference potential for by-passing radio frequency energy therebetween to alterthe energy supplied to the series resonant circuit.

8. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge device having at least an anode, a cathode, and a control electrode, a source of carrier frequency, radio frequency connecting means including coupling means for connecting the cathode to the source of carrier frequency'for exciting the cathode with respect to a point of reference potential, a. load circuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, said series resonant circuit including an inductance element and radio frequency radiating means having a capacitance with respect to said point, said inductance element having first and second ends, effective alternating current connection means for connecting the said first end of the inductance means to the said anode, electrical conducting means for connecting said second end of the inductance means to the said radio frequency radiating means, and means including a capacitance element interconnecting said first end and said point of reference potential for by-passing radio frequency energy therebetween to alter the energy supplied to the series resonant circuit, said coupling means comprising a parallel combination of inductance means and capacitor means.

9. Apparatus for producing a signal modulated carrier frequency, comprising a space dischar e device having at least an anode, a cathode, and a control electrode, a source of carrier frequency, radio frequency connecting means including coupling means for connecting the cathode to the source of carrier frequency for exciting the oathode with respect to a point of reference potential, a load circuit including a series resonantcircuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, said series resonant circuit including an inductance element and radio frequency radiating means having a capacitance with respect to said point, said inductance element having first and second ends, effective alternating current connection means for connecting the said first end of the inductance means to the said anode,'electrica 1 conducting means for connecting said second end of the inductance means to the said radio frequency radiating means, and means including a capacitance element interconnecting said first end and said point of reference potential for by-passing radio frequency energy therebetween to alter the energy supplied to the series resonant circuit, said coupling means comprising a parallel combination of inductance means and capacitor means and including winding means magnetically coupled to the inductance means for connecting the coupling means to the cathode of the space discharge device.

' 10. Apparatus for producing a signal modulated carrier frequency, comprising a space discharge 9 device having at least an anode, a cathode, and a control electrode, a source of carrier frequency, radio frequency connecting means including coupling means for connecting the cathode to the source of carrier frequency for exciting the oathode with respect to a point of reference potential, a loadcircuit including a series resonant circuit connected to the anode of said discharge device and energized by current appearing between said anode and said point, said series resonant circuit including an inductance element and radio frequency radiating means having a capacitance with respect to said point, said inductance eleinent having first and second ends, effective a1- ternating current connection means for connecting the said first end of the inductance means to the said anode, electrical conducting means for connecting said second end of the inductance means to the said radio frequency radiating means, and means including a capacitance element interconnecting said first end and said point of reference potential for by-passing radio frequency energy therebetween to alter the energy supplied to the series resonant circuit, said coupling means comprising a parallel combination of inductance means and capacitor means, the capacitor means comprising a plurality of capacitors having a tapped connection between them for connecting the coupling means to the cathode of the space discharge device.

11. A radio frequency system comprising an impedance, 9, space discharge tube including an electron discharge path, a series resonant circuit having two terminals and consisting of an inductor in series with a capacitor, means to effectively connect in series the impedance, electron discharge path and series resonant circuit, means to supply energy across the impedance at the frequency to which the series circuit is resonant, means to connect a load between the junction of the inductor and the capacitor and a terminal of the series resonant circuit, and means including a capacitor element interconnecting said terminals for by-passing radio frequency energy between said terminals and thereby alternating the energy supplied to the series resonant circuit.

DONALD L. HINGS.

REFERENCES (CITED The following references are of record in the 

